1. Field of Invention
The present invention relates in general to a control circuit of power converter, and more particularly, to a synchronous rectifying control circuit for power converter.
2. Description of Related Art
An offline power converter includes a power transformer to provide isolation from AC line input to the output of the power converter for safety. In recent development, applying the synchronous rectifier on the secondary side of the transformer is to achieve a high efficiency conversion for power converters, such as “PWM controller for synchronous rectifier of flyback power converter” by Yang, et al. U.S. Pat. No. 6,995,991. However, the disadvantage of this prior art is the propagation delay of the switching signal detection and the phase-locking, which degrades the performance of the synchronous rectifier. Besides, the switching current detection causes additional power consumption by the ESR of the output capacitor. The switching signal's phase-lock and the current sense are required to facilitate the synchronous rectifier operation in both continuous mode and discontinuous mode. The object of present invention is to provide a reliable synchronous rectifying circuit, which can achieve higher efficiency. Besides, no current sense device and no phase-lock circuit are required for both continuous mode and discontinuous mode operations.